Northeast Ohio can be one of gloomiest places on the planet during winter, but the lack of sun is not just depressing, it's unhealthy.

Sun on exposed skin naturally produces vitamin D, and our long, dark winters leave many people deficient, a condition that research has connected with heart disease, kidney disease, some cancers and autoimmune diseases.

Most researchers and physicians agree that we need more vitamin D. And because food is generally a poor source, most people turn to pills. But how much do we really need? And how do we know?

The answer depends on who you ask.

The debate

Current recommendations for dailyvitamin D intake were set in 1997 by the Food and Nutrition Board of the Institute of Medicine (IOM), one of the National Academies. They have changed little since doctors figured out about 50 years ago that giving small children cod liver oil (which contains vitamin D) reversed a common bone malformation called rickets, said Bruce Hollis, a nutritional biochemist at the Medical University of South Carolina.

The amount of vitamin D it took to reverse rickets -- 400 international units (IU) --became the recommended dailyintake for children.

Current recommendations from the IOM, which range from 200 IU per day for infants to 600 IU per day for older adults, are based on this original data and the belief that vitamin D is only important to bone health, Hollis said.

But 30 years of research is starting to paint a very different picture of vitamin D: It seems the sunshine vitamin may influence just about every part of the body. Hundreds of studies have shown a correlation between low vitamin D levels and poor health, and others are starting to show a direct relationship between correcting thedeficiency and positive health outcomes.

Most researchers feel the current recommendations are much too low and are calling for change.

The IOM is paying attention. In 2009, the committee started a review of its vitamin D intake recommendations. The report is due to be released this summer, said spokeswoman Christine Stencel.

"Everybody knows that 400 units doesn't do anybody any good," said Reinhold Vieth, a biochemist whose research at the University of Toronto focuses on the role vitamin D plays in osteoporosis and cancers of the breast and prostate.

"You can't tell the difference between when people are taking 400 units or nothing, it's such a tiny dose," he said.

The research

Many other epidemiological studies -- studies that follow groups of people over time to try to connect a health behavior to a particular cause -- have connected low vitamin D levels with pre-eclampsia (high blood pressure in pregnancy); colon, breast and prostate cancer; arthritis; and multiple sclerosis.

Sunshine vitamin basics

What is vitamin D?

It's a fat-soluble vitamin that the body naturally produces when the skin is exposed to ultraviolet light from the sun. The body can store vitamin D in fat and use it when needed.

Where do we get vitamin D?

Most people meet their needs for the vitamin through exposure to sun. Your body can make about 10,000 international units (IU) of vitamin D after just 10 to 15 minutes of exposure to summer sun. It is naturally present in small amounts in very few foods, such as fish, beef liver and egg yolks, and is added to others, such as milk, cheese and bread.

Dietary supplements are the easiest way to get vitamin D in the absence of sun exposure.

Which should I take, D3 or D2?

Vitamin D comes in two forms: cholecalciferol (D3) and ergocalciferol (D2). While there is some debate about whether the two forms are equally potent, most physicians recommend using D3, the form the body makes naturally. If you choose to buy a supplement, check the label for cholecalciferol or D3.

Who is most likely to be deficient?

Breast-fed infants, pregnant and lactating women, people over the age of 50, people with dark skin and those who have limited sun exposure are at high risk for deficiency.

How do you test?

A blood test for vitamin D -- the serum 25(OH)D test -- is drawn just like any other blood test at a routine doctor's office visit. Most insurance will cover the test. The test costs between $250 to $400 without insurance.

Can you get too much?

Excess vitamin D produced by sun exposure is naturally destroyed by the body, but supplements can build up in your body's fat stores. Recent research has shown that children and adults can take 5,000 IU daily with no ill effects, which is much higher than the current recommendations from the Institute of Medicine. Poisonings have been reported, but at prolonged exposures exceeding 40,000 IU a day.

In 2009, researchers at Intermountain Medical Center in Murray, Utah, found that vitamin D deficiency was strongly associated with subsequent cardiovascular disease and death in 27,686 people over the age of 50 followed over a two-year period.

Those results echo an earlier study by Harvard researchers who found that people deficient in vitamin D in a group of about 1,700 Boston residents faced up to twice the risk of stroke or heart attack.

Supporting that research are randomized controlled trials -- considered the gold standard of clinical research trials -- in which people are assigned at random to either a control (often called "placebo") arm or an intervention in order to compare the two.

Harvard Medical School and Brigham & Women's Hospital in Boston are now enrolling 20,000 patients in the largest randomized controlled trial of vitamin D intake to date, called the Vitamin D and Omega-3 Trial. The study, funded by the National Institutes of Health, will measure health outcomes in patients across the country who take a combination of the two supplements (2,000 IU vitamin D and 1 gram fish oil daily) or a placebo over a five-year period.

Hollis and Dr. Carol Wagner, a neonatologist at Medical University of South Carolina, recently finished a six-year, randomized controlled trial examining the effects of different supplementation levels on pregnancy outcomes in 400 women.

While the data hasn't been published yet, Hollis said that higher doses of vitamin D reduced rates of infection, preterm birth and preterm labor among the women who were given either 400 IU (the control group), 2,000 IU or 4,000 IU per day over a 12-week period. And, he said, there wasn't a "single adverse outcome" in the group.

Researchers from the U.S. Department of Agriculture's Western Human Research Center at the University of California, Davis, recently released a study that tried to quantify, for the first time, how much supplemental vitamin D different groups of people need based on how much sun exposure they get during the year.

Their results, published in January in the Journal of Nutrition, showed that people who spend less time in the sun and have darker skin need significantly more vitamin D each day to make up the difference. Based on maintaining a relatively high blood level of the vitamin -- 75 nanograms per milliliter (See "What's normal?") -- the researchers found that people of European ancestry with high sun exposure need about 1,300 IU daily in the winter and people of African ancestry with low sun exposure may need up to 3,100 IU dailyyear-round.

View full sizeThe Plain DealerMost people meet their needs for the vitamin through exposure to sun. Your body can make about 10,000 international units (IU) of vitamin D after just 10 to 15 minutes of exposure to summer sun.

Testing

We live in a northern climate with long, dark winters. So does that mean everyone in Northeast Ohio needs to be tested for vitamin D deficiency?

Yes, says Gina Bayless, chapter president of the American Dietetic Association and dietitian at University Hospitals CaseMedical Center.

"Definitely ask your doctor to check your vitamin D level," she said. "I personally think that everyone should just have it included in their health screening."

Vitamin D levels are checked with a blood test that is usually covered by insurance. Without insurance, the test costs about $350.

The Cleveland Clinic, which does its own lab testing, saw a 46 percent increase in vitamin D tests in 2009 over 2008.

Hollis, the nutritional biochemist, thinks everyone can start supplementing without the test. "I would assume that everyone is deficient without even doing a blood test," he said.

He recommends taking 2,000 to 3,000 IU of vitamin D daily (if you're not already taking a multivitamin) and then getting a blood test a few months later and discussing the results with your doctor to see if you need to adjust your supplement dosage.

"That's probably the most cost-efficient way to go about it," he said, because vitamin D supplements are inexpensive.

While most experts agree that everyone needs to be aware of their vitamin D level, there are some groups who are at particularly high risk for deficiency, Bayless said.

Those groups include adults over the age of 50 (because the body loses its ability to make and absorb the vitamin over time); people with limited sun exposure; people with dark skin (because the pigment melanin blocks the UV rays that produce the vitamin); obese people; pregnant and lactating women; breastfed infants (because their mothers are often deficient); people who have undergone gastric bypass surgery; and those who have certain disorders that make it difficult to absorb fat.

Dr. Tanya Edwards, director of the Center for Integrative Medicine at the Cleveland Clinic, started testing all her patients for deficiency three years ago.

After finding that almost all her patients tested "horribly low, often times undetectable," she began supplementing them with 2,000 IU pills to get them back up to a healthy blood level.

She found it was taking a long time to get their blood levels back into the normal range, so she started getting more aggressive. She has found that she can give some patients what seem like huge doses -- up to 50,000 IU a day -- for short periods to quickly get them back to normal.

In the absence of specific guidelines, physicians like Edwards are treating their patients the best way they know how and using current research to guide them.

Bottom line

Researchers Hollis and Vieth are fairly certain the Institute of Medicine will increase its recommendations for vitamin D intake when it releases its findings this summer.

But Hollis doesn't think the changes will mean all that much for individuals because how much people need will depend on their race, their weight and how much sun exposure they get.

Edwards agrees.

"In my opinion, there is no RDA [recommended daily allowance]," she said.

Test and supplement, she said. The small cost is worth it: "When you think of all the diseases that we can potentially affect by having all patients' vitamin D levels in the healthy range, this is huge in terms of our aging population."

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